1. Technical Field
The disclosure generally relates to illuminating devices, and particularly to an illuminating device incorporating an optical lens, which can improve utilization rate of light emitted from light emitting diodes (LEDs).
2. Description of Related Art
With the continuing development of scientific technology, LEDs have been widely used in illumination devices to substitute for conventional cold cathode fluorescent lamps (CCFL) due to their high brightness, long life-span, and wide color gamut. Relevant subject matter is disclosed in an article entitled “Solid State Lighting: Toward Superior Illumination”, published in a magazine Proceedings of the IEEE, Vol. 93, No. 10, by Michael S. Shur et al. in October, 2005, the disclosure of which is incorporated herein by reference.
Conventional illuminating devices incorporating LEDs generally generate butterfly-type light fields or diffusion-type light fields. Referring to FIG. 14, a diffusion-type light field is shown. The diffusion-type light field is substantially circular. In other words, a part of the light field along an x-direction is substantially the same as a part of the light field along a y-direction. However, this type of light field is not always required in our daily life, such as in a street lamp, which has a strip-type light field requirement. If the diffusion-type light field is applied in the street lamp, part of light will be lost, which decreases utilization rate of the light emitted from the LEDs.
What is needed, therefore, is an optical lens and an illuminating device incorporating the optical lens, which can improve utilization rate of the light emitted from LEDs.